Two-Phase Flow Modeling of Direct Methanol Fuel Cell Anode Compartment

A quasi two-dimensional numerical model was developed to predict the two-phase flow behavior within the anode compartment of direct methanol fuel cells (DMFCs). Different void fraction correlations were employed to examine and estimate the pressure drop, flowrate and methanol concentration variations across the fuel channels. By comparing the modeling results with experimental data, it was discovered that the calculated pressure drop values were highly dependent on the type of void fraction correlation utilized. The best experimental agreement was achieved when using the "separated" flow modeling approach with a void fraction correlation that accounted for surface tension and capillary effects. The "homogenous" flow modeling methodology on the other hand, was found to be inadequate and in all cases, underestimated the two-phase pressure drop. The model demonstrated that the acceleration and gravitational pressure losses had the lowest and highest impact on the overall two-phase pressure drop, respectively. The frictional pressure loss effects only started to appear at higher fuel flowrates and at elevated operating current densities. It was also revealed that increasing the cell's operating current density while maintaining the fuel flowrate, would significantly increase the overall two-phase pressure drop with negligible impact on the net methanol concentration across the anode compartment.